The present invention relates to the field of high speed camera shutters.
The interlens space required to accommodate typical prior art multiple rotary disk, high speed camera shutters is in the neighborhood of 0.4-0.5 inches whereas all that is required to accommodate a two blade shutter provided by the present invention, is an interlens space of about 0.2-0.25 inches, thereby to reduce problems in lens design.
It is thus highly desirable to eliminate the need for a three rotary blade shutter along with a fourth capping shutter generally used for low exposure time aerial cameras, and to provide a two blade shutter which performs at least equally well, so that less interlens space is required to accomodate the shutter mechanism. This is extremely important, since the penalties for increasing the interlens space involve the complexity of the optical design required, such as the provision of aspheric optical surfaces and/or the degradation of photgrammetric performance, namely optical distortion.
In U.S. Pat. No. 3,820,145 to Gallier, a two blade rotary disk shutter is provided having apertures which become aligned at the optical axis at some point during the counter rotation of the blades. When an exposure is desired, the blades are caused to rotate in opposite directions through about one half of a revolution, exposure is effected, and the blades are thereafter rotated another half revolution to their light blocking rest position.
It is an object of the present invention to minimize dynamic disturbances e.g. vibration problems, which result from the application of high impulse forces to the shutters to cause them to rapidly accelerate. The present invention reduces the required acceleration because each shutter is accelerated through almost a full revolution, rather than one-half of a revolution as taught by the above mentioned patent. Since acceleration is reduced, the dynamic disturbances are minimized. A significant difference between the '145 patent and the present invention is that the rotary disks therein are always rotated in the same direction whereas in the present invention the direction of rotation of each disk is reversed after each exposure, thereby to provide for almost a full revolution to accelerate and almost a full revolution to deaccelerate the disks to reduce the high impule drive forces along with related dynamic disturbances.